//173.点名
class Solution {
    public int takeAttendance(int[] records) {
        int left = 0;
        int right = records.length - 1;
        while(left < right){
            int mid = left + (right - left) / 2;
            if(records[mid] == mid){
                left = mid + 1;
            }else{
                right = mid;
            }
        }
        return records[left] == left ? left + 1 : left;
    }
}